"A tennis ball is hollow and composed of inflated rubber covered with a fabric. It is between 2½"and 2 5/8"(6.35 and 6.67 cm) in diameter and weighs between 2 and 2 1/16 ounces (57.7 and 58.5 grams)."

56.7–58.5 g

New Encyclopedia Britannica. 15th ed. 1997.

"The ITF specifies that the ball must be between 2½ inches (6.35cm) and 2 5/8 inches in diameter and between two ounces (56.7 g) and 2 1/16 ounces in weight"

56.7 g

World Book Encyclopedia. Chicago: World Book, 1998.

"It must weigh more than 2 ounces (56.7 grams) but less than 2 1/16 ounces in weight"

56.7–58.5 g

Tennis is an outdoor or indoor game, which is played on a rectangular
court by two persons (known as singles) or by four persons (doubles).
Rackets are used to hit the ball back and forth across a net.
The object of the game is to score points by striking the ball
in a way that an opponent can not successfully return it. The
origins of the game dates back to the Stone Age, when humans first
used their clubs to hit rocks back and forth across barricades
of dirt and stone. The tennis court is 78 feet (23.8 meters) long,
and its divided into equal sides by a net that stands 3 feet (0.9 meters) high at the center of the court. For singles, the court
is 27 feet (8.2 meters) wide. For doubles the width is increased
to 36 feet (11 meters). A tennis ball is hollow and composed of
inflated rubber, covered with a fabric which must be uniform.
Its between 2½ and 2 5/8 inches (6.35 and 6.67 cm)
in diameter and weighs between 2 and 2 1/16 ounces (57.7
and 58.5 grams). Yellow and white balls are used in competition.
When dropped on concrete from a height of 100 inches (2.5 meters),
they must bounce upward from 53 to 56 inches (135 to 147 centimeters).
The serve is the most important stroke in tennis. There are no
weight restrictions on the racket and it is usually strung with
resilient gut or nylon. The surface of the court may be grass,
clay, or some kind of hard material which is usually concrete,
asphalt, synthetic turf, or wood. The court surface is an important
element in tennis because balls bounce higher or lower, faster
or slower, depending on the surface they strike. There is a tendency
to slide on clay while harder surfaces are ideal for quick starts
and stops.